The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Motorized vehicles may include a powertrain that is comprised of a powerplant (e.g., an engine, an electric motor, and/or a combination thereof, a multispeed transmission, and a differential or final drive train. The powerplant produces drive torque that is transmitted through one of various gear ratios of the transmission to the final drive train to drive wheels of the vehicle.
Operation of the powertrain may be regulated by one or more control modules, such as a powertrain control module, based on driver inputs. More specifically, the powertrain control module may receive one or more signals from driver interface devices, such as an accelerator pedal, operated by the driver. Based on the signals it receives, the powertrain control module may regulate the operation of the powertrain to produce a desired drive torque. The powertrain control module may also regulate the operation of the powertrain to maintain a target cruise speed, such as when the vehicle is equipped with a cruise control system.
Vehicles equipped with a cruise control system typically include a cruise control switch that enables the driver to indicate the target cruise speed. In such systems, the driver may indicate the target cruise speed by actuating the switch while driving at the target cruise speed. In turn, the cruise control switch may generate a signal that, along with a wheel speed signal, may be used by the powertrain control module to determine the target cruise speed. The wheel speed signal may be generated using one or more wheel speed sensors that may be included with the vehicle.
In the cruise mode, the powertrain control module may regulate the powertrain to maintain an actual speed of the vehicle within a desired range of the target cruise speed. The actual speed of the vehicle depends on several factors, such as engine drive torque and road grade. Typically, the powertrain control module may regulate the powertrain to maintain the actual vehicle speed within the desired speed range by raising or lowering the drive torque produced by the engine. However, on a downhill grade, the actual speed of the vehicle may continue to increase without the assistance of the drive torque produced by the powertrain. Moreover, the actual speed of the vehicle may exceed an upper threshold speed of the desired speed range.
In this case, the powertrain control module may regulate the powertrain to produce negative drive torque that may be used to decelerate the vehicle and thereby bring the actual vehicle speed within the desired speed range. For example, the powertrain control module may regulate an engine included with the powerplant in a deceleration enleanment mode. In the deceleration enleanment mode, the powertrain control module may inhibit fuel to the engine and thereby cause the engine to generate negative drive torque.
Similarly, in a hybrid powerplant, control module may regulate an electric motor included with the hybrid powerplant in a regeneration mode. In the regeneration mode, rotational energy of the drivetrain generated by the moving vehicle is used to drive the electric motor. The powertrain control module may also regulate the powertrain in a powertrain braking mode. In the powertrain braking mode, the powertrain control module may regulate the transmission to shift into a lower gear, increasing the rotational speed of the powerplant, and thereby increasing the negative drive torque produced by the powerplant.
However, even when operating in one or more of the foregoing modes, the powertrain control module may be unable to inhibit the actual vehicle speed from exceeding the upper speed threshold of the desired speed range.